Devices fabricated from ceramic materials have many important technological applications. For example, they are useful as magnets, capacitors, thyristors, thermistors, as well as in many other applications. Many techniques have been developed for fabrication of these materials and most, if not all, require a high temperature sintering step.
Many types of devices using ceramic materials are electrical devices which require one or more electrical contacts. However, the high sintering temperature, typically 1400.degree. C., greatly restricts the materials that may be used to form the electrodes. As many of the electrode materials are precious metals and since the price of these metals has greatly increased in recent years, methods of ceramic fabrication which permit use of lower sintering temperatures and, thus cheaper electrode materials, would be desirable. Of course, low sintering temperatures are also desirable in the fabrication of other types of devices because, for example, the lower energy costs of said easier compositional control when volatile components are present permitted by the low sintering temperature are desirable.
Multilayer ceramic capacitors are an example of an electrical device for which a lower sintering temperature would be desirable. Processing of multilayer ceramic capacitors typically requires placing an electrode material between layers of ceramic material. Both the ceramic layers and layers of electrode material are cosintered at an elevated temperature in an oxidizing atmosphere. Barium titanate ceramic powders, which are commonly used in multilayer ceramic capacitors, typically require a sintering temperature of approximately 1400.degree. C. At such a relatively high temperature, precious metals such as Ag-Pd alloys, are typically required for the electrode materials. Alternatives, such as an electrode consisting of Ag, cannot be used unless the ceramic material can be sintered at temperatures below the melting point, approximately 962.degree. C., of Ag.
Various approaches have been taken in efforts to lower the sintering temperatures. One approach decreases the sintering temperatures by chemical means by, for example, adding dopants to the ceramic compositions prior to sintering. However, this approach is often undesirable as the dopants may produce deleterious effects on the dielectric properties of the ceramic composition. A second approach prepares the ceramic powder with optimal physical characteristics so that sintering can proceed at low temperatures. One example of this approach was reported in Journal of the American Ceramic Society, 64, pp. 19-22, 1981. This paper reported using de-agglomerated submicron powders of Y.sub.2 O.sub.3 stabilized ZrO.sub.2 which could be sintered at 1100.degree. C. This temperature is approximately 300.degree. C. lower than the normal sintering temperature.